The present invention relates generally to spacecraft, and more particularly, to a photoemission based spacecraft charging sensor for use on spacecraft.
Previously developed charge plates measured the buildup of charge on an electrically isolated dielectric surface. Although this produces voltage data, there is no available voltage reference. As a result, the data produced cannot be easily convened to a spacecraft charging measurement.
A surface charging detector (or charge plate) has heretofore been developed and flown by Lockheed Martin (formerly Martin Marietta). This surface charging detector is described in an article entitled "Integrated Environmental Monitoring System for Spacecraft."
This paper describes an integrated space environmental monitoring system for geosynchronous satellites. The system provides measurements of surface charging, internal charging, and total dose radiation from the space environment. There are two components of the system, including an internal charge monitor and a surface charge detector. The surface charging monitor measures charging by magnetospheric plasma electrons from 3 keV to 20 keV and with worst-case current density from 0.1 to 1 nA/cm.sup.2. The surface charge detector has two components, including a charging plate and control electronics. The charging plate is mounted to the spacecraft structure outside the spacecraft and is exposed directly to the space environment.
However, this prior art monitoring system does not directly measure the electrical potential of a spacecraft in orbit relative to the space environment. Furthermore, this prior art monitoring system does not use photoemission from a photoemitting metal plate as a reference point for voltage readings or provide direct measurements of spacecraft charging.
It would be therefore be advantageous to have an improved photoemission based spacecraft charging sensor for use on spacecraft.